1. Field of the Invention
This invention relates to an electrically heated windshield wiper, and, more particularly to a such a wiper in which the electrical heater is supported by secondary pressure frames and enveloped by a shroud for preventing the accumulation of ice, sleet and snow on the shroud as well as the squeegee element of the windshield wiper.
2. Description of the Prior Art
The operation of a windshield wiper on curved windshields particularly windshields with complex curvatures is impaired when there accumulates in an environment characterized by such adverse circumstances as subfreezing or even sub-zero temperatures, ice, sleet, and snow. The impairment to the operation is attributed according to the underlying principal of the present invention to the loss of flexibility preventing uniform contact between the windshield wiper and the curved windshield. As found in U.S. Pat. Nos. 2,656,448 to Lentz; 2,746,077 to Higgins; 3,408,678 to Linker; 3,530,525 to Abel; 3,574,881 to Temple; 3,619,556 to Deibel; 3,667,083 to Linker; 4,325,160 to Burgess; 4,360,941 to Mabie; and 4,670,933 to Toplenszky it is well known in the art to embed or bring into intimate contact a heating element with a flexible wiper element of a windshield wiper assembly designed to operate on curved windshield of an automobile. In U.S. Pat. No. 2,903,732 there is disclosed a wiper blade construction for de-icing a windshield by forming a gap between two wiper blades so that the gap between the blades forms a passageway for hot air generated by a heating element situated within an insulator sleeve provided within a cylindrical wiper body. In the operation of the wiper, the heating element prevents ice from forming on the windshield and the reduction of visibility thereby.
While it is known in the art to provide an electrical heater in a windshield wiper blade, the blade construction is such that the heater is always placed at a site for the purpose of heating the squeegee element of the blade. The purpose to be served by the heater placement according to the prior art is that of keeping the squeegee element free of ice and snow, however, according to the present invention such measures are ineffective to prevent the accumulation of ice and snow on the main pressure frame as well as the secondary pressure frames whereby the functioning by these frames is diminished impairing the efficient wiping contact between the squeegee and the windshield. Since ice and snow is allowed to accumulate on the pressure frames, there is a likelihood that the accumulations will approach the squeegee. This necessitates that the heating element being in continuous use in the inclement weather to maintain the squeegee free of ice and snow accumulations. The life expectancy of the elastomer material forming the squeegee is shortened due to thermal degradation. A need therefore is seen to exist for a wiper blade construction which will avoid the need to heat the squeegee element and at the same time improve the resistance to accumulations of ice and snow on the wiper.
Accordingly, it is an object of the present invention to provide an improved wiper for windshields and back windshield of an automobile having an electrically resistive heater mounted on pressure frames of the wiper blade and maintain in a protective environment provided by a shroud of which the squeegee element is wholly external thereof.
It is a further object of the present invention to provide an improved construction for a wiper for a windshield of a back windshield of an automobile which will allow modification existing wipers without modification and replacement of existing parts.